The present invention relates to a single lens reflex camera, and more particularly, to an output device for range information for use in an interchangeable lens adapted to be detachably mounted on a camera.
In a single lens reflex camera, range information is required for effecting an automatic focussing operation. A mechanical transfer device has been widely utilized in the past to obtain range information from the lens side. However, such device has the disadvantage of being large-sized, complicated and inaccurate. A a result, an arrangement in which information signals are transmitted to a camera body has been proposed (Japanese Laid-Open Patent Publication Sho 54/1979-108628). The proposed arrangement, however, lacks the capability of expanding the scope of information since signals are limited to only that information which is transmitted from the lens side and a prescribed sequence for transmitting signals can not be varied. When it is desired to obtain information from a camera system other than a lens in the same way, a number of input lines are required, resulting in that the arrangement increases in size and becomes complicated.
In view of the foregoing, camera systems in which an arithmetic unit of a microcomputer (hereinafter referred to as a CPU) is separately disposed in each of the systems have been proposed by the assignee of the present invention (Japanese Laid-Open Patent Publication Sho 60/1985-26324). Even in this proposal, however, there is no practical solution to the problem of reading range information of an interchangeable lens and transmitting the range information to a camera body.
Outputs relating to range information of an interchangeable lens fall into two categories, absolute and relative range information. Absolute range information in an autofocussing operation is represented by an output of a signal corresponding to a range obtained by reading a rotation preset position of a range ring as shown in, for example, Japanese Laid-Open Patent Publication Sho 50/1975-67650. Relative range information refers to the amount by which a present position is away from a reference position. The use of relative range information, which can be produced only by a comblike electrode, for example, advantageously simplifies a construction of an output device for range information of an interchangeable lens. On the other hand, although absolute range information may be conveniently used in a single lens reflex camera serving as a system camera, it leads to a complicated structure and therefore is rarely used.